1. Field of the Invention
The present invention relates generally to backflow prevention devices and, more particularly, to a plumbing fixture for connection between a sewer connection and an appliance or equipment drain line for preventing backflow by interposing an air gap therebetween.
2. Description of the Prior Art
There is an inherent danger in connecting the drains of equipment or appliances directly to a sewer system. This is because some condition might occur which permits the backflow of sewer fluids through the drain lines into the equipment to contaminate it. For this reason many governmental entities have established codes that must be complied with before an equipment drain can be connected to a sewer system. Such codes commonly require that a device be inserted between each equipment drain line and the sewer system to prevent backflow. Such backflow can be caused, in the case of an equipment drain line, by an unexpected increase in liquid pressure in the sewage system or an unexpected decrease of liquid pressure at the drain line. In either case there is the possibility that highly contaminated sewage could be drawn into equipment connected to the drain line.
In particular, equipment used in restaurants, hospitals, supermarkets and industry typically drain their waste liquids through drain lines into the building drainage system which is connected to the public sewer system. Most plumbing codes require these equipment drain lines to be indirect drain lines, i.e., they may not connect directly with the building drainage system or the public sewer system. Rather, the drain lines must dispose of their liquid wastes by discharging into a plumbing fixture which itself is directly connected to the building drainage or public sewer systems. The plumbing fixture must generally provide an air gap between the equipment drain line and the drain standpipe or hub which is connected to the building drainage or public sewage systems.
Attempts to provide such backflow protective devices have focused on relatively complicated devices, such as valves which have numerous moving parts capable of being fouled by solids in the discharged liquids. Other proposed devices include baffled chambers requiring machined parts and/or close tolerances, all of which are impractically expensive for most applications. Even those devices which appear to be relatively simple require assembly of several parts and/or several threaded connectors, which make them uneconomical for the numerous everyday discharge connections such as might be encountered from supermarket freezer drains, soda machine drains, and the like. What is required for most day-to-day applications is a device in which the air gap is pre-set and which is truly simple, one-piece, capable of injection molding to facilitate production at low unit costs, devoid of moving parts and inherently incapable of failing to operate to prevent backflow.